1. Field of the Invention
This invention relates to a ligand and a metal complex, more particularly to a ligand and a metal complex made from the ligand and useful as a magnetic resonance imaging (MRI) contrast agent, for example a blood pool contrast agent or a targeting contrast agent.
2. Description of the Related Art
MRI is used in in vivo imaging techniques for medical diagnosis. The image signal intensity generated in MRI depends not only on the amount of targeted tissue water, but also on the spin-lattice relaxation time (T1) and the spin-spin relaxation time (T2) of protons of the targeted tissue water. Reduction of T1 leads to an increase in the image signal intensity. Contrast agents are commonly used in MRI for improving image contrast due to their effect on reducing T1.
In Y. M. Wang, et al., J. Chem. Soc., Dalton Trans, 1998, pp. 4113-4118, there is disclosed a ligand of 3,6,10-tri-(carboxymethyl)-3,6,10-triazadodecanedioic acid (TTDA). The publication also shows that TTDA exhibits a better effect on reducing T1 than that of diethylene triamine-pentaacetic acid (DTPA).

In Y. M. Wang, et al., Helv. Chim. Acta, 2002, 85, 1033, there is disclosed a modified TTDA, (S)-4-Bz-TTDA, which has a formula:

Although (S)-4-Bz-TTDA is useful as a hepatobiliary MRI contrast agent, it is not suitable for MRI diagnosis of other targets.
Hence, there is a need to find a contrast agent that has a greater effect on reducing T1 and to develop a contrast agent for MRI diagnosis of various targeted tissues or organs, especially for blood pool contrast agents and targeting contrast agents exhibiting bioactivity.